Drafting device

ABSTRACT

Curves of different radii may be generated by displacement of a point in a tracing plate element relative to an imaginary fixed center of curvature remote from the plate element. A selected pair of slots disposed at an angle to each other on the tracing element receives a pair of guide pins fixedly spaced from each other by sliders adjustably positioned on a base element. Tracing apertures are formed in the tracing element between the slots to receive a pencil or other drawing implement in contact with a planar surface while tracing an arc.

United States Patent [191 Streander June 11, 1974 DRAFTING DEVICE Prima Examiner-John W. Huckert 75 I tzGeo W.St d,Al nven or N. a rean er amoglordo Assistant Examiner-Jon W.Henry Attorney, Agent, or Firm-Clarence A. OBrien; Har- [73] Assignee: Design Systems, Inc., Alamogordo, vey B. Jacobson N. Mex.

22 Filed: Nov. 5, 1971 2 f (m ZST d b d urves o l erent ra 11 may e generate y is [2!] Appl' 1967051 placement of a point in a tracing plate element relative to an imaginaryfixed center of curvature remote [52] US. Cl. 33/27 F from the p at m nt- A sel ted pair of slots dis- [51] Int. Cl. B43k 9/00 Posed at an ngl to a h ther on the tracing element [58] Field of Search 33/27 D, 27 E, 27 F, 27 G, receives a pair of guide pins fixedly spaced from each 33/27 H, 27 R other by sliders adjustably positioned on a base element. Tracing apertures are formed in the tracing ele- [56] References Cit d ment between the slots to receive a pencil or other UNITEDSTATES PATENTS drawing implement in COIlIflCt Wllih a planar surface 861,400 7 1907 Sheridan 33/27 F whlle tracmg 2,552,215 5/1951 Rekdahl .L 33/27 F 9 Claims, 4 Drawing Figures Penc/I 2*;- 3 1 3a "6;" 53a3 a 0% I l i'l'i l i 'i l l'i l o n ul'l'i'l'l'i' i i'i i'l' v liismalumea /l I Bllfilllll n llllllll/llllihllllilll[llllilllill J/ l il|l|| I2 30, t 20 4 3A;

. 1 DRAFTING DEVICE This invention relates'to a'drafting device for drawing curves of different and varying radii. The present invention is unique in that it provides a drafting instrument through which curves of constant radii may be drawn in a precise manner. The drafting instrument is particularly useful in drawing a circular are from one point to another and to enable the draftsman to more accurately generate a curve without reliance on'approximations and/or the use of French curves.

In accordance with the present invention, the, drafting device of the present invention in an initial position may be aligned with a point on a planar drawing surface on which an arc is to be drawn. The instrument includes an elongated base plate element which is adapted to be held stationary at one point while a tracing is displaced by means of a pencil or other drawing tool in contact with the drawing surface. A selected pair of guide slots on the tracing element are engaged by pivot pins projecting from overlying carriers that are adjustably fixed relative to each other by a pair of sliders mounted on the base element. The spacing between the pivot pins and the angular relationship between the pair of guide slots, predetermine the radius of a circular arc. The insersections of the guide slot paths lie on definite circular arcs having radii values that are multiples of the radius selected by adjustment of the spacing be tween sliders on the base element. A plurality of apertures are formed in the tracing element at the intersections of the guide slot paths in order to receive a pencil tracing the curve on the planar surface against which the base element is held.

These together with other objects and advantages which will become subsequently apparent reside in the details of construction and operation as more fully hereinafterdescribed and claimed, reference being had to the accompanying drawings forming a part hereof, wherein like numerals refer to like parts throughout, and in which:

FIG. 1 is a top plan view of the drafting device of the present invention.

FIG; 2 is a transverse sectional view taken substantially through a plane indicated by section line2-.2 in FIG. 1. i j

FIG. 3 is a transverse sectional view taken substantially through a plane indicated by section line 3-3 in FIG. 1.

FIG. 4 is a geometrical diagram illustrating the mathematical parameters associated with the drafting instrument of the present invention.

Referring now to the drawings in detail, the drafting instrument is illustrated in its entirety inFIG. 1 and is generally denoted by reference numeral 10. The drafting instrument includes an elongated base plate element 12, a tracing plate element 14 and a pair of slider components 16. The elements 12, 14 and sliders 16 are made of a suitable rigid, plate-like material, preferably a transparent plastic. The sliders, 16 are slidably mounted on the base element 12 while the tracing element 14 is interconnected with the base element 12 through the sliders as will be explained hereafter.

The base element 12 is in the form of an elongated straight edge having parallel spaced edges 18 and 20 along which slidable movement of sliders 16 are guided. Located intermediate the opposite ends of the base element 12 on the edges 18 and 20, are a pair of ,on which the two sliders 16 are guided for slidable movement by means of a pair of pins 24 on each slider riding on the edge 18. The index line extends through the center of curvature of the are being generated.

Each slider 16 includesalongitudinal slot 26 through which the threaded shank 28 of a lock element 30 extends. The shank is threadably connected to the base element 12 so that when the headportion'32 of the lock element is tightened against the slider, it will be held in its adjusted position on the base element. Scales 33 may accordingly be placed on the base element 12 which are visible through the sliders 16 in order to precisely guage the positions of the sliders on the base element by means of the vernier indices 34 formed on the sliders. In this manner, the user may precisely set the device for a desired radius without referring to mathematical tables or resorting to calculations.

Each of the sliders includes a carrier extension 36 which overlies the tracing element 14 to which the sliders are operatively connected by a pair of pivot pins 38.

The pivot pins pivotally and slidably connect the sliders to the tracing element 14 by means of a selected pair of guide slots 40 into which the pivot pins 38 project.

The tracing element 14 is provided with parallel spaced, longitudinal rim portions 42 as more clearly seen in FIGS. 2 and 3 in sliding contact with the planar surface 44 with which the undersurface of the base element 12 is held in contact in order to prevent smearing of ink when used to draw curves. A plurality of aper tures 46 are formed in the tracing element aligned along a line perpendicular to the longitudinal axis of the tracing element. As more clearly seen in FIG. 2, the apertures 46 are tapered and are adapted to receive therethrough, the point of a pencil 48 or a drawing pen through which a curve is adapted to be generated on the surface 44 in response to displacement of the tracing element 14 relative to firmly held points at lock elements 30 by moving the drawing pencil or pen. Displacement of the tracing element is constrained because of engagement between the pair of pivot pins 38 and the guide slots 40. The pairs of guide slots are disposed and spaced so that a wide range of arcs may be drawn.

In order to utilize the drafting device, a tracing point on the surface 44 from which a curve of predetermined radius is to be drawn is located below a selected one of the tracing apertures 46. Thedesired spacing of pivot pins 38 is then obtained by adjusting the positions of the sliders 16 on the base element 12 equidistant from the index notches 22 and locking the sliders at the adjusted positions by means of the lock devices 30. The pivot pins 38 are then inserted into a selected pair of guide slots 40 on opposite sides of the tracing point. In the illustrated embodiment, four different pairs of guide slots are provided, each being disposed at a different angle to eachother. The sliders when engaged with the guide slots through the pivot pins, are then moved together with the base element until the tracing apertures 46 are aligned with the index notches 22 thereby establishing the initial position for the drafting device, in which the tracing point is centered between the pivot pins 38. With the base element 12 then held stationary at points 30 on the planar surface 44, the tracing element is displaced by means of the pencil 48 projecting through one of the apertures 46 in contact with the surface 44 thereby generating a circular arc.

In FIG. 4, point C represents the intersection between the guide paths associated with a selected pair of slots 40 for an initial position of the drafting device while points A and B represent the pivot points at which the pivot pins 38 are located in the initial position. The pivot pins A and B and the intersection point C of the guide paths accordingly lie on a circular are 50 having a radius (r) and a center of curvature at point 0. The radius of the are 50 will be predetermined by the fixed spacing (2k) between the pivot points established by the adjusted positions of the sliders 16 as aforementioned and the angular relationship between the selected guide paths. The angular relationship between the guide paths is denoted by the external angle (28) as shown in FIG. 4. Thus, from the geometrical relationships shown in FIG. 4:

r k/sin 2B When (k) and (,8) are constant, (r) is constant.

In accordance with the present invention, an arc 50 as shown in FIG. 4 is generated by movement of'a tracing point C at a selected aperture 46 in response to dis placement of the device as aforementioned. When the tracing element is displaced, the base element 12 remains fixed while the point of intersection C between the selected guide paths traces the circular are 50 in view of the constraint imposed by the interengagement of the pivot pins 38with the selected pair of guide slots 40. Asa result of this constraint, the radial line 54 extending from the center 0, is angularly displaced to a position 54' as shown in FIG. 4.

In the example illustrated in FIG. I, the scales 33 are calibrated so that the sliders 16 may be spaced to obtain arc radii that are a multiple of a factor value shown on the scales. The multiple is determined by the guide slots 40 selected corresponding to the four uppermost apertures 46 at which the guide'slot paths intersect. The five lowermost apertures 46 provide a step variation from the factor value indicated on the scales 33. For example, with the sliders 16 set at a minimum value of three inches, a three inch radius arc will be drawn by a pen inserted in the aperture 46 fourth from the top, denoted 1X. Placement of the pen in the uppermost aperture (8X) will draw an arc of 24 inches while the five lowermost apertures produce a reduction inradius of 0.2 inch steps to a minimum radius of 2 inches. Thus, a range of radii between 2 and 48 inches is available with the instrument shown. It will also be apparent that the movable element 14 provides facilities through guide slots 40 and apertures 46 for selecting multiples of a radius set by locking of the sliders 16 on the base element 12.

The foregoing is considered as illustrative only of the principles of, the invention. Further, since numerous modifications and changes will readily occur to those skilled in the art, it is not desired to limit the invention to the exact construction and operation shown and described, and accordingly, all suitable modifications and equivalents may be resorted to, falling within the scope of the invention.

What is claimed as new is as follows:

I. A drafting device for generating curves of different radii comprising a base element having calibrated scales formed thereon, adjustable means mounted on the base element for establishing a pair of pivot points lying on an are having a predetermined radius of curvature, a rigid tracing element, guide means on the tracing element and engageable with the adjustable means for constraining movement of the tracing element relative to both of said pivot points simultaneously, and tracing means mounted on the tracing element for establishing a third point movable along said are in response to said constrained movement of the tracing element, said guide means comprising a plurality of pairs of slots formed in said tracing element, said pivot points being movable within a selected one of said pairs of slots.

2. The combination of claim 1 wherein said tracing means comprises a plurality of openings spaced between the slots and adapted to receive a curve tracing implement therethrough.

3. The combination of claim I wherein the spacing of the pivot points and the angular relationship ofthe slots predetermine a constant radius of an arc interconnecting the pivot points.

4. The combination of claim 3 wherein said tracing means is located equidistant between said pivot points in an initial position of the tracing element relative to the base element.

5. The combination of claim 1 wherein said base element includes parallel spaced edges along which the adjustable means is guided and index notches formed in said edges in alignment with the tracing line in the initial position of the tracing element.

6. The combination of claim 1 wherein said tracing means is located equidistant between said pivot points in an initial position of the tracing element relative to the base element.

7. The combination of claim 6 wherein said base element includes parallel spaced edges along which the adjustable means is guided and index notches formed in said edges in alignment with the tracing means in the initial position of the tracing element.

8. A drafting device for generating curves of different radii comprising a base element, adjustable means mounted on the base element for establishing a pair of pivot points fixedly spaced relative to the base element, a tracing element, guide means establishing guide paths on the tracing element for constraining relative movement between the pivot points and the tracing element along said guide paths, and means mounted on the tracing element for tracing said curves in response to said 'relative movement, said adjustable means including a pair of sliders movably mounted on the base element, lock means for holding the sliders in adjustably fixed positions on the base element, a pair of pins engageable by the guide means at said pivot points and pin carrier formations, extending from the sliders in overlying relation to the tracing element, from which the pins project into the guide means, said guide means comprising a plurality of pairs of slots formed in said tracing element along said guide paths, said pins being received within a selected one of said pairs of slots.

9. A drafting device for generating curves of different radii comprising a base element, adjustable means mounted on the base element for establishing a pair of pivot points fixedly spaced relative to the base element, a tracing element, guide means mounted on the tracing element and engageable with the adjustable means for constraining movement of the tracing element relative to both of said pivot points simultaneously, and tracing able means in coplanarrelation to each other, said guide means comprising a plurality-of pairs of slots formed in the tracing element along guide paths intersecting at points lying on a radial line. 

1. A drafting device for generating curves of different radii comprising a base element having calibrated scales formed thereon, adjustable means mounted on the base element for establishing a pair of pivot points lying on an arc having a predetermined radius of curvature, a rigid tracing element, guide means on the tracing element and engageable with the adjustable means for constraining movement of the tracing element relative to both of said pivot points simultaneously, and tracing means mounted on the tracing element for establishing a third point movable along said arc in response to said constrained movement of the tracing element, said guide means comprising a plurality of pairs of slots formed in said tracing element, said pivot points being movable within a selected one of said paiRs of slots.
 2. The combination of claim 1 wherein said tracing means comprises a plurality of openings spaced between the slots and adapted to receive a curve tracing implement therethrough.
 3. The combination of claim 1 wherein the spacing of the pivot points and the angular relationship of the slots predetermine a constant radius of an arc interconnecting the pivot points.
 4. The combination of claim 3 wherein said tracing means is located equidistant between said pivot points in an initial position of the tracing element relative to the base element.
 5. The combination of claim 1 wherein said base element includes parallel spaced edges along which the adjustable means is guided and index notches formed in said edges in alignment with the tracing line in the initial position of the tracing element.
 6. The combination of claim 1 wherein said tracing means is located equidistant between said pivot points in an initial position of the tracing element relative to the base element.
 7. The combination of claim 6 wherein said base element includes parallel spaced edges along which the adjustable means is guided and index notches formed in said edges in alignment with the tracing means in the initial position of the tracing element.
 8. A drafting device for generating curves of different radii comprising a base element, adjustable means mounted on the base element for establishing a pair of pivot points fixedly spaced relative to the base element, a tracing element, guide means establishing guide paths on the tracing element for constraining relative movement between the pivot points and the tracing element along said guide paths, and means mounted on the tracing element for tracing said curves in response to said relative movement, said adjustable means including a pair of sliders movably mounted on the base element, lock means for holding the sliders in adjustably fixed positions on the base element, a pair of pins engageable by the guide means at said pivot points and pin carrier formations, extending from the sliders in overlying relation to the tracing element, from which the pins project into the guide means, said guide means comprising a plurality of pairs of slots formed in said tracing element along said guide paths, said pins being received within a selected one of said pairs of slots.
 9. A drafting device for generating curves of different radii comprising a base element, adjustable means mounted on the base element for establishing a pair of pivot points fixedly spaced relative to the base element, a tracing element, guide means mounted on the tracing element and engageable with the adjustable means for constraining movement of the tracing element relative to both of said pivot points simultaneously, and tracing means mounted on the tracing element fixedly spaced relative to the guide means for developing an arc in response to said constrained movement of the tracing element, said base and tracing elements being made of thin rigid plate material interconnected by the adjustable means in coplanar relation to each other, said guide means comprising a plurality of pairs of slots formed in the tracing element along guide paths intersecting at points lying on a radial line. 